Conventionally known flush valves included self-generating type valves whereby an electrical generating unit for supplying power to the built-in electromagnetic valve is added to a flush valve for supplying water to sanitary equipment such as a toilet (refer to Patent Document 1, for example). The flush valve of Patent Document 1 comprises: a main valve body for opening and closing a flow path between a primary side flow path and a secondary side flow path; a sub-valve body (electromagnetic valve) disposed in a bypass flow path communicating between a back pressure chamber communicating with the primary side flow path and the secondary side flow path; and an electrical generating unit disposed in the secondary side flow path on the downstream side of the main valve body.
In the flush valve, because the closing force pressing on the closing side due to pressure inside the back pressure chamber is normally greater than the opening force pressing on the opening side by pressure inside the primary side flow path, the main valve body is held in the closed position. However, the flush valve is activated in response to manipulation of a switch by a user, or to activation of a human presence sensor.
The start of the flush valve operation results in the sub-valve body being driven by electrical power received from a secondary battery (rechargeable battery) such as a capacitor, displacing the sub-valve body from the closed position to the open position. This puts the bypass flow path in an open state; water in the back pressure chamber passes through the bypass flow path and flows out to the secondary side flow path, which is at a lower pressure than the back pressure chamber. This draining of water from the back pressure chamber causes the closing force which had been impinging on the main valve body to become smaller than the opening force, so the main valve body starts to move toward the open position, and water starts to flow from the primary side flow path to sanitary equipment connected to the secondary side flow path. The flow rate is then maximized when the main valve body reaches an open position.
In the generating unit, water flows to the secondary side flow path, and spouting current therefrom turns an impeller to generate electricity, which is then stored by the secondary battery. The main valve body closes in response when the sub-valve body closes after a predetermined time, thereby stopping spouting.
Note that sanitary equipment such as toilets require the supply of a high force spout flow from the flush valve to reliably discharge waste. Therefore the main valve body must be moved rapidly to an open position (full lift position) at which maximum instantaneous flow can be obtained. This rapid movement can be achieved by quick water draining from the back pressure chamber through operation of the sub-valve body.